Abstract: The boost fuel enricher is used with internal combustion engines, either carbureted or fuel-injected, that are equipped with compressors, i.e., turbocharged or supercharged, in order to enrich the air/fuel ratio when the engine is under boost. The boost fuel enricher is a diaphragm pressure valve with an adjustable throat. The diaphragm is subject to atmospheric pressure on one side, and senses inlet air pressure in the air intake passage on the other side. When inlet air pressure exceeds atmospheric pressure, the valve opens to admit additional air-fuel mixture into the air intake passage through a venturi in the air intake passage. The throat is made adjustable by sliding block valves in the fuel passage.